Coating for ferrous alloys



Patented June 21, 1938 2,121,606

UNITED STATES PATENT oFFrcr.

COATING FOR FERROUS ALLOYS Leon McCulloch, Pittsburgh, Pa", assignor toWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation of Pennsylvania No Drawing. Application July 31, 1936,

, Serial No. 93,743

Claims. (Cl. 134-44) This invention relates generally to coatings forThe boric acid employed in the solution has of ferrous alloys andparticularly to a coating for itself no binding or adhesive value, butwhen magnetic material. chemically reacted with magnesium oxide, the

An object of this invention is the provision of boric acid and magnesiumoxide form a strong a lubricating and refractory coating for magadhesivefilm-forming substance somewhat simi- 5 netic material. lar to waterglass, which is quite effective Another object of this invention is theproviin maintaining the colloidal aluminum silicate sion of a coatingfor ferrous alloys which will on the surface of the sheets of magneticmatefunction as a die lubricant, a refractory, and an rial. Since thecoating is often employed in coninsulating material. junction withinsulating liquids, the boric acid 10 Another object of this inventionis the provi in the binder is of special value to the coating, sion of acoating for magnetic material which since it has been proven throughexperiments will not-cause deterioration of insulating liquids. thatboric acid retards the deterioration of in- Other objects will becomeapparent from the sulating fluids, such as oil.

following description. In practice,.the coating employe'd comprises Inelectrical apparatus, such as transformers, 100 parts by weight ofwater, 1 to 100 parts by the magnetic material employed as the corememweight of the colloidal aluminum silicate, 1 to 10 hers is fabricatedfrom ferrous alloys by rolling parts by Weight of boric acid, andmagnesia in an ingot of the ferrous alloy to a predetermined an amountranging from 1 to 100% of the weight thickness, shearing or punching therolled maof the boric acid employed. The choice of the 20 terial intosheets of a desired size and then anamount of the colloidal aluminumsilicate denealing the sheets of ferrous alloy to develop pends upon thematerial employed and the anits magnetic properties. In fabricating themagnealing temperature to which the coating .will netic material, it isdesired to provide a coating be subjected.

on the surface of the alloy that will function Where low annealingtemperatures of the or- 25 as a lubricant during the shearing orpunching der of 725 C. are employed, the refractory masteps, and as arefractory material between the terial, bentonite, will substantiallyprevent the sheets to prevent the sheets from fusing togethersticking'of the sheets of ferrous alloy. In the during the anneal.bentonite coatings, 1.to 50 parts by weight of Since the sheets ofmagnetic material are often bentonite gives a stifl mixture whenemployed in 30 employed in conjunction with an insulating liqthesolution within the ranges given hereinbefore uid, the lubricatingandrefractory coating on and produces satisfactory results. the sheetsmust not react with the insulating Where the coating is to be subjectedto a high liquid to cause sludging or otherwise impair the annealingtemperature, it is sometimes desirable insulating properties of theliquid. In addition to employ kaolin as the refractory material in- 5 tothese properties, it is desired that the coating stead of bentonite.This is because kaolin, being provide insulation for the sheets ofmagnetic a purer grade of colloidal aluminum silicate, is material toprevent eddy currents in the assemmore refractory than bentonite. Inorder to probled apparatus. duce a coating of the same constituency aswhen 40 In practicing this invention, a coating is probentonite isemployed, it is necessary to employ 4o vided that will satisfy therequirements hereinmore of the kaolin than the bentonite with a beforeenumerated. The coating of this invengiven solution. As much as 100parts by weight tion comprises a mixture of a colloidal aluminum of kalin may b employed ith th b i acidsilicate of a clay-like nature, suchas bentonite magnesium id l ti given h r i b or kaolin, in a solut on ofb ric d an ma Suflicient magnesium oxide is employed in so- 45 nes um Od The colloidal aluminum Silicate 1S lution with boric acid to renderthe solution a refractory material and when applied as a substantiallyneutral. This solution is a good coating n Sheets of ferrous alloy willprevent binding agent for the refractory materials. When the sheets fromsticking when subjected to an applied to the sheets of ferrous alloy,the boric annealing temperat In Order to prevent the acid solutioncontaining the refractory material 50 refractory material from flakingand blowing off may be easily dried leaving a glassy film on the of thesheets of ferrous material during the surface of the sheets. This filmfunctions as at annealing, the refractory material is carried inlubricant for the shears or dies employed in a binder comprising asolution of boric acid, magshearing or punching the sheets to thedesired nesium oxide and water. size. The magnesium oxide in thecoating, in '55- addition to reacting with the boric acid to make thesolution neutral, further functions as a. refractory material.

Some of the preferred bentonite coatings are given in the followingtable:

Parts by weight Bentonite 17. 15 9. 6 8. Boric acid 5 8. Magnesium oxide.036 29 Water 100. 00 100. 00 Red oxide oi ir n 1. 7

In the above table, it is noted that coating #100 contains 1.7 parts byweight of red oxide of iron. The red oxide of iron is added to thesolution in order to give a distinctive color to the coating. Inaddition to giving a particular color to the coating, the iron oxidealso functions,

when the coating is applied to the sheets of ferrous alloy, as arefractory and aids in preventing the sheets from sticking during theanneaiing process. Red oxide of iron may or may not be added to thecoating as desired.

Where the sheets of ferrous alloy are subjected to annealingtemperatures of 1100 C, or higher, a more refractory coating than thebentonite coatings listed above may be desired. A kaolin coatingcomprising parts by weight of Georgia kaolin, 2 parts by weight of boricacid, .15 part by weight of magnesium oxide, and parts by weight ofwater is particularly satisfactory at the higher temperatures since itdoes not fuse,

but instead prevents the sheets from sticking for lubricating the shearsduring the shearing step in addition to acting as arefractory to preventthe sticking of the sheeiz. Under test, it is found that the filmdeposited on the sheet when the solution is evaporated provides sumcientinsulation for preventing eddy currents. The coatings further do notcause deterioration of the insulating liquids with which they areemployed.

Although this invention has been described with reference to aparticular embodiment thereof, it is, of course, not to be limitedthereto except insofar as is necessitated by the prior art and the scopeof the appended claims.

I claim as my invention:

1. A coating for ferrous alloys comprising from 1 to 100 parts by weightof a colloidal aluminum silicate selected from the group consisting ofbentonite and kaolin in a solution consisting of about 100 parts by.weight of water, from 1 to 10 parts by weight of boric acid andmagnesium oxide in an amount ranging from 1% to 100% of the weight ofthe boric acid.

' 2. A coating for ferrous alloys comprising from 1 to 100 parts byweight of kaolin in a solution consisting of about 100 parts by weightof water,

from 1 to 10 parts by w i ht of boric acid and magnesium oxide in anamount ranging from 1% to 100% of the weight of the boric acid.

3. A coating for ferrous alloys comprising from 1to50partsbywl8htofbentoniteinasolution consisting of about 100 parts by weight ofwater, from 1 to 10 parts by .weight of boric acid and magnesium oxidein an amount ranging from 1% to 100% of the weight of the boric acid.

4. A coating for ferrous alloys comprising about 17 parts by weight ofbentonite, about 5.75 parts by weight of boric acid, about 0.45 part byweight of magnesium oxide and about 100 parts by weight of water. g

5. A coating for ferrom alhys comprisingabout80partsbyweightofholimabout2parts water.

LION llcOUILOCH.

